Sweep air system for membrane air dryer

ABSTRACT

A membrane air dryer is located inside a compressed air reservoir. A sweep air system includes a sweep control valve upstream of the dryer, and a sweep vent that is open to atmosphere.

BACKGROUND

The present invention relates to a compressed air reservoir and an air dryer and a sweep air system for the dryer. In the illustrated embodiments, the invention is applied to an air braking system of a vehicle, such as a truck. Such a system typically includes an air compressor and a reservoir for storing the compressed air. Compressed air is drawn from the reservoir to provide for application of air brakes and/or other vehicle devices. Such a system also typically includes an air dryer for removing moisture from the compressed air. It is known to use a membrane dryer to remove moisture from the compressed air, and to then remove the moisture from the membrane dryer by a flow of sweep air across the membrane dryer.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of portions of a compressed air braking system, including a reservoir and a membrane dryer located in the reservoir;

FIG. 2 is an enlarged view of the dryer and portions of the reservoir of FIG. 1, including elements of the sweep control system;

FIG. 3 is a view similar to FIG. 2 of a different reservoir and dryer system;

FIG. 4 is a view similar to FIG. 1 of a further braking system;

FIG. 5 is a view similar to FIG. 2 of portions of the system of FIG. 4; and

FIG. 6 is a view similar to FIG. 2 of yet another system.

DETAILED DESCRIPTION

The invention is applicable to air systems of various different types and configurations, and for various different vehicles. As two examples, the invention is applicable to commercial trucks and to locomotives. FIG. 1 is a schematic diagram of portions of a compressed air system 10. The system 10 includes a reservoir 12. A membrane dryer 14 is located in the reservoir 12. An inlet line 16 directs air from a compressor (not shown) into the dryer 14 in the reservoir 12, through a check valve 18. An outlet line 20 directs dried air from the reservoir 12 to vehicle systems, such as brakes, etc. A portion of the dried air is directed through a line 22 to a sweep control valve 24, which controls flow of sweep air to the dryer 14, as described below. The sweep control valve 24 constitutes control means located upstream of the sweep side of the dryer 14, for selectively enabling flow of sweep air to the dryer, as described below.

In the embodiment of FIGS. 1 and 2, the dryer 14 is a bore-fed dryer that includes a shell 30 (FIG. 2) with an elongate cylindrical configuration centered on an axis 32 of the reservoir. The shell 30 includes an imperforate outer tube 34 and a perforated inner tube 36.

A tubular bundle 40 of hollow fibers 42 is supported in the shell 30 between the outer and inner tubes 34 and 36. Each fiber 42 is a membrane having a bore though which air to be dried can be passed, to remove water from the air. The bundle 40 of fibers 42 forms a membrane assembly in the dryer 14. At each end of the bundle 40 is an epoxy plug 44, or other suitable material, that seals the spaces between the various fibers 42, to provide a barrier between the high pressure side of the dryer 14 and the low pressure side of the dryer.

In the approximate center of the inner tube 36 is a stopper or plug 46, which may be made of an elastomeric material, such as rubber. The stopper 46 impedes or blocks air flow longitudinally through the inner tube 36 and forces air to flow through openings 48 in the inner tube and thus to move radially outward into the bundle 40 of fibers 42.

An inlet housing 50 is located at one end of the dryer 14, supported on the end wall of the reservoir 12. The inlet housing 50 has a compressor inlet 52 in fluid communication with the check valve 18. The compressor inlet 52 opens into an inlet chamber 56 that directs compressed air into the bores of the fibers 42. The inlet housing 50 also has a centrally located sweep air outlet chamber 58, that opens from the inner tube 36 of the shell 30. The sweep air outlet chamber 58 has a sweep vent 60 for venting air and water to the atmosphere. The sweep vent 60 is open to atmosphere, as described below in detail.

The opposite end 62 of the dryer 14 is also supported on the reservoir 12, at a location within the reservoir. In this particular embodiment, the opposite end 62 of the dryer 14 is supported by an internal support 66 of the reservoir 12, on the axis 32. The internal support 66 is configured as a sweep air inlet pipe that is physically connected with the reservoir 12. The pipe 66 has a fitting 68 that places the interior of the pipe in fluid communication with a sweep air nozzle 70 that is itself in communication with the inner tube 36 of the dryer shell 30. Thus, the internal support 66 for the dryer 14, which is the inlet pipe, doubles as a sweep air feed conduit.

The sweep air inlet pipe 66 is connected with the sweep control valve 24. The sweep control valve 24 in this particular embodiment is shown located on the outside of the reservoir 12, although it could be located elsewhere in other embodiments. The sweep control valve 24 is connected with the interior of the reservoir 12 through a supply pipe 74. The sweep control valve 24 is controlled by a control signal shown schematically at 76, which may be an electrical control line. The system 10 may, for example, include an electronically operated controller (not shown) that, in a known manner, opens and closes (fully or proportionally) the sweep control valve 24. The system 10 thus provides for sweep air flow from the reservoir 12, through the supply pipe 74, into and through the sweep control valve 24, through the conduit 66 and the nozzle 70, and into the dryer 14.

When the system 10 is charging, compressed air from the compressor flows through the check valve 18, the compressor inlet 52, and the inlet chamber 56, into the bores of the fibers 42, and is dried therein. Water that is removed from the air migrates to the outside of the fibers 42. The dried air from the fibers 42 of the fiber bundle 40 flows through the opposite (outlet) end 62 of the dryer 14 and into the reservoir 12, where it is stored.

The sweep air is provided to remove the water from the outside of the fibers 42. When the sweep control valve 24 is open, dry air flows from the reservoir 12 through the supply pipe 74, through the sweep control valve 24, and through the inlet pipe 66, into the inner tube 36 of the shell 30. This air constitutes the sweep air for the dryer 14. The inner tube 36 of the shell 30, together with the spaces between the several fibers 42, forms a sweep air chamber of the dryer 14. The sweep air flows through the perforations 48 in the inner tube 36 to surround the various fibers 42 and pick up moisture from them. The sweep air transports the moisture to the sweep air outlet chamber 58 and then to the sweep vent 60. The sweep air, and any moisture that it has picked up, exits through the sweep vent 60.

The sweep vent 60 is open to atmosphere. There is no valve located in the fluid flow path between the membrane fibers 42 and atmosphere (downstream of the fibers), blocking flow out of the sweep vent or closing it off. The fiber bundle 40 in the dryer 14 is continuously, or constantly, exposed to atmosphere through the sweep vent 60. The sweep vent thus vents sweep air whenever there is sweep air flowing through the dryer 14, that is, when the sweep valve 24 is open. When the sweep control valve 24 is closed, accordingly, sweep air flow is not flowing through the dryer and venting through the sweep vent 60, even though the sweep vent is open.

When the sweep valve 24 is closed, the open condition of the sweep vent 60 means that moist air does not accumulate at the location of the sweep vent or in any associated piping, moisture that might freeze in cold weather and disrupt operation; rather, the moist air can migrate out of the dryer 14 through the open sweep vent, because there is some exchange or flow of air into and out of the dryer through the open vent. In that sense, it can be said that the sweep vent 60 vents sweep air continuously. Also, because of the continuous, or constant, exposure of the membrane bundle 40 to atmosphere, there is little or no moisture accumulation in the form of condensation on the shell side of the dryer 14, which condensation could decrease efficiency of the dryer.

To enable the sweep vent 60 to be left open, the flow of sweep air through the dryer 14 is controlled upstream of the sweep vent, or there would be a constant flow of sweep air through the dryer, potentially discharging the reservoir 12. In the illustrated embodiment, as one example, the sweep control valve 24 is located external to the reservoir 12, upstream of the dryer 14, and in fluid communication with both the interior of the reservoir and the sweep feed conduit 66. Dry air is piped from the reservoir 12 to the sweep valve 24, which controls the sweep air flow, and into the conduit 66. From the conduit it flows into the sweep side of the dryer 14.

Proportional control of sweep air flow is possible with this system 10. Proportional control requires throttling of the sweep air. Any attempt to throttle sweep air flow exhaust, downstream of a membrane dryer, produces back pressure on the low pressure side of the dryer. This decreases dryer performance. In contrast, when the sweep control valve is located upstream of the sweep side of the dryer, closing off sweep flow does not create back pressure to the detriment of membrane drying performance.

One preferred range for sweep air flow is from about 15% to from about 20% of the main air flow. Excess sweep air flow would waste dried air in the vehicle. Too little sweep air flow would not remove enough moisture from the air being dried for use in the vehicle. Of course, vehicles during operation have varying main air flow because the compressor is driven in relation to engine speed, which varies, and because the demand on the system (drawing air out of the reservoir) varies significantly over time.

Because the dryer 14 is located inside the reservoir 12, it does not require a separate space or mounting location on the vehicle. In addition, an assembly in which the dryer 14 is mounted on the axis 32 of the reservoir 12 is less difficult to fabricate than one in which the dryer is mounted on the bottom side wall of the reservoir, and provides for simpler operation of the sweep vent.

Another advantage of the system of FIGS. 1 and 2 is that there is no significant pressure cycling on the membrane dryer 14. Specifically, the high pressure (upstream) side of the dryer membrane 40 is pressurized to full system pressure at all times. The low pressure (downstream) side of the membrane 40 is at atmospheric pressure at all times. Therefore, there is no significant cycling; pressure drop is limited to the difference (about 20 psi) between compressor cut in pressure, and compressor cut out pressure. Therefore, the pressure variation in the bores of the fibers 42, over time, is limited, which can help to increase the longevity of the fibers.

FIG. 3 illustrates another embodiment of the invention, also for a locomotive (but usable elsewhere), but having a different sweep air inlet structure. Specifically, the sweep air inlet connection inside the reservoir (as in the embodiment of FIGS. 1 and 2) is eliminated. Instead, sweep air flows into an end cap 80 that includes both a sweep air inlet 82 and a compressor air inlet 84, as well as a sweep vent 86. As in the embodiment of FIGS. 1 and 2, dry air from the dryer 88 flows into the reservoir 90. The inner end 92 of the dryer is supported inside the reservoir 90, on the axis 94, by a spider 96. In this system the sweep air connection inside the reservoir 90 is eliminated, and all connections are external to the reservoir and are at one point only, for ease of servicing.

FIGS. 4 and 5 illustrate another embodiment of the invention, for a commercial truck but usable elsewhere. The system 100 includes a governor 102 that responds to reservoir (system) pressure through a line 104 and that turns the compressor on and off accordingly, via a control line 106. The system pressure is also directed to the sweep valve 108 through line 105 so that, when the pressure is low enough to turn the compressor on, the sweep valve is also opened. The sweep valve 108 is located upstream of the dryer and of the sweep vent 109, which is open to atmosphere.

FIG. 6 illustrates another embodiment of the invention, specifically with a reverse flow path. In the system 110 shown in FIG. 6, overall flow is reversed so that wet compressed air flows first into the reservoir 112. At one end of the reservoir 112, wet compressed air flows into the reservoir through an inlet 124. Wet air flows from the reservoir 112 into the dryer 126 to be dried during the times when the system 110 pulls air (from a reservoir outlet 116, through the dryer).

A sweep valve 120 receives sweep air supply through a connector of a governor 122. The sweep air supply is not controlled by the governor. The sweep air is directed into the dryer at an inlet 118 and exits via a sweep air vent 128. The sweep valve 120 is thus located upstream of the dryer and of the sweep vent 128, which is open to atmosphere. There is also provided an automatic liquid drain valve 130 from the reservoir in addition to the sweep vent 128. 

1. Apparatus comprising: a reservoir for storing compressed air; a membrane dryer located inside the reservoir for drying the compressed air, the dryer having a sweep side across which sweep air can flow; and a sweep control valve upstream of the sweep side of the dryer for controlling flow of the sweep air into the sweep side of the dryer.
 2. Apparatus as set forth in claim 1 comprising a sweep vent downstream of the sweep side of the dryer, the sweep vent being open to atmosphere.
 3. Apparatus as set forth in claim 2 wherein the sweep vent provides continuous exposure of the sweep side of the dryer to atmosphere when the sweep control valve is open and when the sweep control valve is closed.
 4. Apparatus as set forth in claim 2 wherein sweep air from the sweep control valve flows through the dryer and the sweep vent when the sweep control valve is open and sweep air does not flow through the dryer and the sweep vent when the sweep control valve is closed.
 5. Apparatus as set forth in claim 1 wherein the dryer is bore fed and the shell side of the membrane is the sweep side.
 6. Apparatus as set forth in claim 1 wherein a first end of the dryer is supported on an end wall of the reservoir, and a second end of the dryer is supported on an internal support in the reservoir, the internal support comprising a sweep air conduit.
 7. Apparatus as set forth in claim 6 wherein the sweep air conduit directs sweep air from the sweep control valve to the sweep side of the dryer at a location inside the reservoir.
 8. Apparatus as set forth in claim 7 wherein the sweep vent is in a housing that also includes a compressor inlet of the reservoir, air from the compressor inlet being directed into the dryer and thence into the reservoir.
 9. Apparatus comprising: a reservoir for storing compressed air; and a membrane dryer located inside the reservoir for drying compressed air that flows to the reservoir, the dryer having a sweep side; the dryer having a generally cylindrical configuration and being generally coaxial with the reservoir; an outer end of the dryer being supported on an end wall of the reservoir; an inner end of the dryer being supported on an internal support in the reservoir, the internal support constituting a sweep air conduit.
 10. Apparatus as set forth in claim 9 further comprising a sweep control valve located upstream of the sweep side of the dryer, and wherein the sweep air conduit directs sweep air from the sweep control valve to the sweep side of the dryer at a location inside the reservoir.
 11. Apparatus as set forth in claim 10 further including a second conduit for directing dry air to the sweep control valve as sweep air, the output of the sweep control valve being directed into the sweep air conduit in the reservoir and into the sweep side of the dryer at the inner end of the dryer.
 12. A system as set forth in claim 9 wherein the dryer includes a sweep vent that is open to atmosphere.
 13. A method comprising the steps of: directing compressed air into a membrane dryer that has a sweep side and that is located inside a reservoir, to dry the air; directing sweep air into a sweep control valve; controlling the sweep control valve to selectively enable the sweep air to flow from the sweep control valve to the sweep side of the dryer to remove moisture from the dryer; and venting sweep air from the sweep side of the dryer through a sweep vent.
 14. A method as set forth in claim 13 wherein the step of venting sweep air comprises venting sweep air through a sweep vent that is open to atmosphere.
 15. A method as set forth in claim 14 wherein the step of venting sweep air comprises venting sweep air through a sweep vent that provides continuous exposure of the sweep side of the dryer to atmosphere when the sweep control valve is open and when the sweep control valve is closed.
 16. Apparatus as set forth in claim 15 wherein sweep air from the sweep control valve flows through the dryer and the sweep vent when the sweep control valve is open and sweep air does not flow through the dryer and the sweep vent when the sweep control valve is closed.
 17. A method as set forth in claim 13 wherein the step of controlling the sweep control valve comprises selectively enabling or blocking or proportionally enabling the flow of dry air as sweep air through the sweep control valve to the sweep side of the dryer.
 18. A method as set forth in claim 13 wherein the step of proportionally enabling the flow of dry air as sweep air through the sweep control valve comprises providing a flow of sweep air that is at least about 15% of the main air flow through the dryer.
 19. A method as set forth in claim 13 wherein the step of proportionally enabling the flow of dry air as sweep air through the sweep control valve comprises providing a flow of sweep air that is no more than about 20% of the main air flow through the dryer.
 20. A method as set forth in claim 13 wherein the step of proportionally enabling the flow of dry air as sweep air through the sweep control valve comprises providing a flow of sweep air that is in the range of from about 15% to about 20% of the main air flow through the dryer.
 21. A method as set forth in claim 13 further including the step of directing sweep air from the sweep control valve through a sweep air feed conduit to the sweep side of the dryer, the sweep air feed conduit supporting the dryer inside the reservoir.
 22. Apparatus comprising: a reservoir for storing compressed air; a membrane dryer located inside the reservoir and having a sweep side for receiving a flow of sweep air to remove moisture from the dryer; and control means located upstream of the sweep side of the dryer, for selectively enabling flow of the sweep air to the sweep side of the dryer.
 23. Apparatus as set forth in claim 22 further comprising venting means that is open to atmosphere and located downstream of the sweep side of the dryer.
 24. Apparatus as set forth in claim 23 wherein the venting means comprises a sweep vent that is open to atmosphere.
 25. Apparatus as set forth in claim 24 wherein the sweep vent provides constant exposure of the sweep side of the dryer to atmosphere when the control means enables flow of sweep air and when the control means does not enable flow of seep air.
 26. Apparatus as set forth in claim 24 wherein sweep air from the sweep control valve flows through the dryer and the sweep vent when the control means enables flow of sweep air and sweep air does not flow through the dryer and the sweep vent when the control means does not enable flow of sweep air.
 27. Apparatus as set forth in claim 22 wherein the control means comprises a sweep control valve that is selectively controllable to enable or to block the flow of sweep air to the dryer.
 28. Apparatus as set forth in claim 27 wherein the sweep control valve is selectively controllable to proportionally enable the flow of sweep air to the dryer.
 29. Apparatus as set forth in claim 28 wherein the sweep control valve is selectively controllable to provide a flow of sweep air that is at least about 15% of the main air flow through the dryer.
 30. Apparatus as set forth in claim 28 wherein the sweep control valve is selectively controllable to provide a flow of sweep air that is no more than about 20% of the main air flow through the dryer.
 31. Apparatus as set forth in claim 28 set forth in claim 10 wherein the sweep control valve is selectively controllable to provide a flow of sweep air that is in the range of from about 15% to about 20% of the main air flow through the dryer. 